Radio pulse transmission system



June 10, 1947. D a BOND RADIO PULSE TRANSMISSION SYSTEM Filed Sep'h. 25, 1942 -Illllul Whfmxxl A mwhs mnnl l Lilli Donald e3. and

Cttorncu Patented June l0, 1342 OFFICE RADIO PULSE TRANSMISSION SYSTEM Donald S. Bond, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application September 25, 1942, Serial No. 459,621

Claims.

My invention relates to radio pulse-echo systems and particularly to systems which include electro-mechanical indicating or control apparatus that is responsive to the time delay between transmission and reception of a radio pulse.

Radio pulse-echo systems which are utilized to determine distance or altitude by measuring the time required for a radio pulse to travel from a transmitter to a reilecting object and back to a receiver located near the transmitter are well known. Such travel time is usually determined by means of a cathode ray indicator which calibrated to read distance directly. For some applications it is desirable to have the distance indicated by a mechanical indicator such as a dial and pointer. Also it may be desirable to have other mechanism controlled or driven in accordance with the echo pulses.

An object of the present invention is to provide an improved means for and method of indicating distance in a pulse-echo system.

A further object of the invention is to provide an improved electro-mechanical system that is responsive to the elapsed time between transmission of a pulse and reception of the pulse after reflection.

In one preferred embodiment of the invention the received echo pulses are caused to trigger a square wave generator for producing a square wave current that is next converted into a sine wave current. This sine wave current is applied to a phase comparison circuit together with a phase reference sine wave current that is supplied from the pulse transmitter or from an oscillator feeding the pulse transmitter through a variable phase shifter. The output of the phase comparison circuit drives a reversible motor that is coupled to the variable phase shifter. r1"he motor and the phase shifter are driven in one direction or the other until the phase difference between the two sine wave signals is 90 degrees, at which time the current supplied to the motor from the comparison circuit is zero and the motor stops. Thus an indicator coupled to the inctor or phase shifter may be calibrated to read distance directly.

The invention will be better understood from the following description taken in connectionv with the accompanying drawing in which the single figure is a block and circuit diagram of one embodiment of the invention.

Referring to the drawing, the`pulse transmitter of the system comprises a sine wave oscillator I0 operating at a frequency fo which supplies a sine wave signal to a Wave shaping circuit I2 which reshapes the signal to produce electrical pulses I3. The pulses |3 modulate a radio transmitter 4 whereby pulses of radio energy are radiated to earth or to some other reflecting surface or object.

The reilected or echo pulses are received and demodulated in a radio receiver i6. The output pulses are applied to a square wave generator |8, such as a multivibrator, which is triggered to produce a current of a square wave form I9. The square wave current i9 is passed through a lter or tuned circuit 2| to convert it into a sine wave current 22 which is amplied by an amplifier 23 and impressed upon the input circuit transformer 24 of a phase discriminator 26.

A sine wave reference current 21 is supplied from the oscillator I0 through a variable phase shifter 28 and an amplifier 29 `to the phase discriminator 26. It should be understood that the phase shifter may be located between the oscillator lll and the wave shaping circuit I2, if desired, instead of in the position illustrated. Another suitable location for the phase shifter 28 is in the receiving circuit following the filter 2|.

The phase discriminator 26 comprises a pair of diodes 3| and 32 connected in balanced relation. The diode plates are connected to opposite ends of the secondary of transformer 24 while the diode cathodes are connected to opposite ends of the serially connected resistors 33 and 34 and inductance coil 35. A filter capacitor 30 is connected in shunt to resistors 33 and 34. The coil 35 is included in the circuit to provide a derivative voltage whereby hunting is reduced as eX- plained in my Patent 2,208,623, issued July 23, 1940.

The phase reference current 21 is applied to the discriminator 26 by connections to the midpoints of the secondary of transformer 24 and of the coil 35. The reference current 21 (after passing through phase shifter 28) and the sine wave current 22 representative of the received pulses are impressed across the diodes 3| and 32 in additive relation whereby the direct current output of the diodes depends upon the phase relation of the two signals at the discriminator 26. If this phase relation is degrees, the diode outputs are equal and opposite in phase whereby the D.C. voltage between the cathode and of resistor 33 and the cathode end of resistor 34 is zero.

A balanced amplifier comprising amplifier tubes 36 and 31 has its input circuit direct current connected across the diode resistors 33 and 34. Its output circuit is connected through a transformer 38 to one winding 39 of a reversible 3 motor el which may be of the two phase type. The other motor winding l2 is connected to a power supply d3 circuit through a transformer 44.

In order to supply to the motor winding 39 a current that is 90 degrees out of phase with the current supplied to the motor winding 42, a voltage is fed into a phase shifting circuit 4S from the power supply 43. The voltage from circuit 156 is applied to the input ccuit of amplier tubes 3G and 3l' by connections to the junction point of grid resistors 4'! and 48 and to the am# pliier tube cathodes.

From the foregoing it will be evident that ne current is supplied to the meter winding 39 when the grids of tubes 36 and 37 are at equal bias potentials, this being the condition when the current 222V from the receiver is 90 degrees out of phase with respect to the reference current sup,- plied' from amplier 29. Any departure -from this 90 degree phase relation will cause the motor 4l to run in one direction or the other.

The rotor of motor 4| is mechanically coupled to the variable phase shifter 28 as indicated by the broken line 52 so that the phase shifter is driven until the reference current is brought into the 90 degree phase relation with the receiver output signal 22 at which time the motor il stops. By coupling an indicating device such as a rotatable pointer 53 to the rotor 5l of the motor, and by properly Calibrating the apparatus, the distance from the transmitterreceiver unit to the reflecting object may be read directly from a scale 54 associated with the pointer 53. The rotor 5l preferably is connected to the phase shifter 23 and to the pointer 53 through gear reduction units not shown.

TheV phase shifter 28, which may be similar to a goniometer, need not'be described in detail since suitable phase Shifters are well known.v A phase shifter of the goniometer type is described, for example, in copend'ing application Serial No. 421,071, filed November 29, 1941, in the name of Ray D. Kell and entitled Indicator and/or control system. While one specic phase vdiscriminator circuit hasbeen described, it should be understood thatthe invention is not limited tok the use of this particular circuit.

I claim as my invention'z` l. .The method of operating a pulse-echo system which comprises transmitting pulses of energy to a reflecting object, receiving said pulses after reection from said object, converting said received pulses into a sine wave current, producing a phase reference sine wave current at the transmitter, mixingA the two sine wave currents and producing a control eurent that is a measure of their phase difference, and shifting the phase of the two sine wave currents with respect to each other in accordance with the value of said control signal to bring the amount of said phase shift to a predetermined'rvalue whereby said amount of phase shift is a measure of the distance to said reflecting object.

2. The method of operating a pulse-echo system which comprises transmitting pulses of energy to a reflecting` object, receivingv said pulses after reflection from said object, converting said received vpulses into a sine ywave current,f'pr` o` ducing a phase reference sine wave current, shifting the phase of the phase referencefcurrent with respect to the transmitted pulses, mixing the two sine wave currents and producing a control current that is a measure of their phase diierence, and varying the amount of said phase shift in accordance with the value of said control current to bring the amount of said phase' shift to a predetermined value whereby said amount of phase shift is a measure of the distance to said reflecting object.

3. A pulse-echo system comprising means for transmitting pulses of energy to a reilecting object, a receiver for receiving said pulses after reflection Ifrom said object, means for converting said received pulses into a sine wave current, a phase discriminator circuit, means for applying said sine wave current to said discriminator circuitQmeans for obtaining a phase reference current of sine wave form from said transmitting means, variable phase shifting means for shifting the phase of said reference current and said rst sine wave current with respect to each other, means for applying the reference current to said discriminator circuit whereby the output thereof varies in accordance with the phase relation of the two currents applied thereto, a motor that is mechanically coupled to said phase shifting means, and means for driving said motor in accordance with the output of said discriminator.

4. A pulse-echo system comprising means for transmitting pulses of energy to a reecting object, a receiver for receiving said pulses after reflection from said object, means for converting said received pulses into a square wave current, means for converting said square wave current into a sine wave current, a phase discriminator circuit, means for obtaining a phase reference current of sine wave form from said transmitting means, variable phase sluiting means for shifting the phase of said reference current and said rst sine Wave current with respect to each other, means for applying said two sine wave currents to said discriminator circuit whereby the output thereof variesk in accordance with the phase relation of the two currents applied thereto, a motor that is mechanically coupled to said phase shifter, and means for driving said motor in accordance, with the output of said discriminator.

5, A pulse-echo system comprising means for transmitting pulses ofV energy to a reflecting object, a receiver for receiving said `pulses after reflection from said object, means. for converting said; received pulses. into a square wave current, lter means for converting said square wave current into a sine wave current, a phase discrirninatQrv circuit, means for applying said sine wave current to said discriminator circuit, means for obtaining av phase reference current of sine Wave form from 'said transmitting means, variable phase shifting means for. shifting the phase of said reference current with respect to the transmitted pulses, means` for applying the reference current to said discriminator circuit whereby the output thereof varies in accordance with the phase relation. of the two currents applied thereto, a motor that is mechanically. coupled to said phase shifting means, and means for driving said motor in accordance with the output of said discriminator.

DONALDS. BOND. 

